Studies on membrane biogenesis are mainly concerned with the sites of synthesis and assembly of phospholipids and enzymatic marker proteins. The approach utilizes combined biochemical, cytochemical, and electron microscopic techniques and the major studies involve secretory cells of the ducklings' salt gland stressed by salt ingestion. Removal of plasma membrane during distressing, an amplified example of turnover, is also being studied. Another system evincing rapid biogenesis of membranes is the thylakoid membranes of chloroplasts of Chlamydomonas (Y-1) exposed to light, and of 137 plus (wild type) in developmental cycles. Related studies involve NaKATPase to trace the pathway of insertion as well as enzymes involved in phospholipid synthesis, phosphatidic acid phosphatase and CDP amine and other diglyceride transferases. Some of these phospholipid methods are applied to studies concerning the biogenesis of pulmonary surfactant.